Method of preconditioning comestible materials using steam/water static mixer

ABSTRACT

Methods of preconditioning comestible materials such as foods or feeds include the step of separately injecting steam and water into a static mixer in order to create a blend, which is then injected into the materials within a preconditioner barrel. The methods yield increased cook values in the preconditioned materials, with a reduction in evolved steam from the preconditioner.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention is broadly concerned with improved apparatus forthe injection of plural fluids into extrusion system processingcomponents, such as preconditioners and extruders. More particularly,the invention is concerned with such apparatus, alone or in combinationwith extrusion system processing components, which include injectorvalves, preferably with interconnected static mixer sections, toefficiently inject steam/water mixtures (and other optional fluids, ifdesired) using greatly simplified equipment.

Description of the Prior Art

Extrusion cooking systems have long been used for the processing ofvarious types of comestible products, such as human foods or animalfeed. Such systems have a number of different components, but theprincipal processing components are an upstream product preconditionercoupled to a downstream extruder. In the preconditioner, initially dryingredients are typically mixed with water and/or steam and oil in orderto moisturize and partially pre-cook the ingredients. The preconditionedproducts are then fed into the extruder where the materials aresubjected to increasing levels of temperature, pressure, and shear, andare extruded from restricted orifice die structure. In some instances,additional steam and/or water is injected into the extruder barrelduring processing, as an extrusion aid and to facilitate completecooking and forming of final products.

Conventional preconditioners generally include an elongated vessel orhousing having one or two elongated, axially rotatable shafts thereinhaving outwardly extending mixing elements or beaters thereon. As theingredients are advanced toward the outlet of the housing, moisture inthe form of steam or water is injected at separate locations along thehousing length. Consequently, these preconditioners are equipped withcorresponding manifolds with injectors leading to the interior of thehousing. Moreover, delivery hoses are usually secured to the manifoldsfor delivery of moisture. This complicated apparatus can be difficult toservice and clean, and requires sophisticated manual operator control toassure proper moisturization at the different injection locations. Forexample, U.S. Pat. No. 7,906,166 illustrates multiple-injectormoisturization apparatus secured to a preconditioner housing. In othercases, additional such assemblies are used for injection along virtuallythe entire length of the preconditioner housing.

These conventional preconditioners tend to generate and vent asignificant quantity of steam during use thereof. This is a seriousproblem for processors, owing to the fact that this escaping hot steamcan readily mix with food particulates, creating a contamination problemas the materials coat the extrusion system components and the adjacentenvironment. This contamination is aesthetically unpleasant, and cancreate serious microbiological contamination problems as well. Moreover,the evolution of excess steam is a very inefficient waste of thermalenergy.

The injectors used with typical preconditioners are of relatively smalldiameter, usually on the order of one-half-five-eighths inch, and canhave relatively long lengths of over 6 inches. As such, it is quitecommon for the injectors to become partially or completely pluggedduring operation of the preconditioners, requiring down time andmaintenance/cleanup.

Many of these problems are duplicated where extruders are equipped withconventional injectors, although not usually to the same extent aspreconditioners. Nonetheless, it can be difficult to control andcontinuously operate an extruder where injection/contamination issuesare faced.

There is accordingly a need in the art for improved injection apparatuswhich can be used with preconditioners and/or extruders in order to moreefficiently inject plural fluids, while minimizing the plugging andcontamination problems endemic with conventional extrusion systems,while optimizing the use of thermal energy.

SUMMARY OF THE INVENTION

The present invention overcomes the problems outlined above and providesimproved apparatus for injection of fluids into extrusion systemprocessing components, such as a preconditioner housing and/or anextruder barrel. The preferred apparatus comprises a fluid static mixersection including an elongated, tubular casing having a plurality offluid inlets, a stationary mixing assembly within the casing andoperable to mix plural fluids, and an outlet for delivering mixed fluidsfrom the static mixer. The preferred apparatus further comprises aninjector valve including a fluid inlet operably coupled with the staticmixer outlet, a mixed fluid outlet, shiftable control valve structure,and an actuator operably coupled with the valve structure for selectiveshifting thereof. The overall apparatus has structure for permittingcoupling of the valve fluid outlet to an extrusion system componentselected from the group consisting of a preconditioner housing and anextruder barrel.

The composite static mixer/injector valve apparatus can be used with apreconditioner and/or an extruder for injection of fluids. In the caseof a preconditioner, only a single composite apparatus is normallyrequired, and in the case of an extruder, plural apparatus can be usedadjacent the inlet end of the extruder barrel.

Although the composite apparatus is preferred, the invention is not solimited. That is, a preconditioner may be provided including fluidinjection apparatus made up of an injector valve alone permittingselective injection of fluid into the preconditioner housing; theinjector valve includes a fluid inlet, a fluid outlet, and shiftablevalve structure for selective fluid flow control from the valve inlet tothe valve outlet.

In order to minimize or eliminate plugging of the fluid injectionapparatus, the axial distance between the valve outlet and the innersurface of the preconditioner housing should be less than about 3inches, advantageously less than about 1 inch, and most preferably lessthan about one-half inch. Similarly, the diameter of the fluid-conveyingstructure of the injection apparatus should be relatively large,preferably at least about 1 inch. The combination of the large diameterfluid conveying-structure together with the short valve injectiondistance assures essentially plug-free operation of the preconditioner.

These same considerations apply in the context of fluid injectionapparatus for extruders, i.e., the fluid-conveying components and theinjection path lengths should be designed using the same diameter/lengthparameters recited above in the case of preconditioners.

While composite fluid injector valve/static mixer section injectionapparatus is preferred, improvements can be realized using thesecomponents separately, i.e., a preconditioner or extruder may beequipped only with the injector valves of the invention, or converselyuse can be made of static mixer sections without the need for injectorvalves.

The invention is primarily concerned with steam and/or water injectioninto extrusion components. However, other ingredients or additives canbe injected separately or along with moisture, such as fats, colorants,emulsifiers, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a preconditioner in accordance with theinvention, equipped with an improved fluid injection assembly includinga fluid valve injector and a static mixing section;

FIG. 2 is a fragmentary top view of the preconditioner illustrated inFIG. 1;

FIG. 3 is a vertical sectional view taken along the line 3-3 of FIG. 2;

FIG. 4 is a perspective view of the access door of the preconditioner ofFIG. 1, including a mounting bracket for the valve injector of the fluidinjection assembly;

FIG. 4A is an enlarged, fragmentary view illustrating a fluid injectionvalve assembly mounted on the door bracket of FIG. 4;

FIG. 5 is a side view of a fluid injection assembly comprising anupright static mixing section, but without the use of a fluid valveinjector;

FIG. 6 is a side elevational view of the internal mixing element forminga part of the static mixer section;

FIG. 7 is a perspective view of a twin screw extruder having four fluidinjection assemblies mounted on the extruder barrel, with the assembliescomprising fluid valve injectors, without the use of static mixingsections;

FIG. 8 is a sectional view of a barrel section of the twin screwextruder, and illustrating four of the valve injectors of the inventionmounted on a barrel section of the extruder;

FIG. 9 is an enlarged, fragmentary, sectional view of one of the valveinjectors depicted in FIG. 8, and illustrating further details of thevalve injector; and

FIG. 10 is a view similar to that of FIG. 7, but illustrating fluidinjection assemblies including both fluid valve injectors and staticmixing sections.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to FIGS. 1-4, a preconditioner 20 is illustrated, equippedwith a composite fluid injection assembly 22 mounted thereon fordelivery of mixed fluids, such as steam and water, to the interior ofthe preconditioner. The preconditioner is of the type described in U.S.Pat. No. 7,906,166, which is fully and completely incorporated byreference herein.

Broadly, the preconditioner 20 includes an elongated mixing housing 24with a pair of parallel, elongated, axially-extending, rotatable mixingshafts 26 and 28 within and extending along the length thereof. Theshafts 26, 28 are operably coupled with individual, digitallycontrolled, variable speed/direction drive devices (not shown). Thepreconditioner 20 is adapted for use with a downstream processing devicesuch as an extruder or pellet mill, and is used to moisturize andpartially cook comestible materials, such as human foods or animalfeeds.

In more detail, the housing 24 has an elongated, transversely arcuatesidewall 30 presenting a pair of elongated, juxtaposed,intercommunicated chambers 32 and 34, as well as a material inlet 36, alower material outlet (not shown), and a vapor vent 38. The chamber 34has a larger cross-sectional area than the adjacent chamber 32, as willbe readily apparent from a consideration of FIG. 3. The sidewall 30 hasfour, hingedly mounted access doors 40, and the assembly 22 is securedto the rearmost access door 40 communicating with chamber 34. Thisaccess door 40 is equipped with a mounting plate 42 having an injectionaperture 43 which extends through the door and presents an innermostinjection opening 43 a (FIG. 4A). Of course, mounting plate 42 or othersimilar hardware can be affixed to other portions of the sidewall 30, atthe discretion of the designer. The opposed ends of housing 24 areequipped with end plates 44 and 46, as shown.

Each of the shafts 26, 28 has a plurality of outwardly-extending mixingelements 48 and 50 thereon which are designed to agitate and mixmaterial fed to the preconditioner, and to convey the material frominlet 36 towards and through the lower outlet. The elements 48 areaxially offset relative to the elements 50, and the elements 48, 50 areintercalated (i.e., the elements 50 extend into the cylindricaloperational envelope presented by shaft 26 and elements 48, and viceversa). Although the elements 48, 50 are illustrated as beingsubstantially perpendicular to the shafts 26, 28, the invention is notso limited; moreover, the elements 48, 50 are adjustable in both lengthand pitch, at the discretion of the user. It will be seen that the shaft26 is located substantially along the centerline of chamber 32, and thatshaft 28 is likewise located substantially along the centerline of thechamber 34.

The composite fluid injection assembly 22 of this embodiment broadlyincludes a fluid injection valve assembly 52 and a static mixing section54, and is designed to inject a plurality of mixed fluids intopreconditioner 20, such as steam/water or steam/water/additives. Asexplained in greater detail below, the assembly 22 simplifies theequipment required for fluid injection, is more sanitary, increases theenergy efficiency of the preconditioner, and results in higher levels ofmoisture and/or cook in the preconditioned products, as compared withconventional fluid injection equipment.

The injection valve assembly 52 (FIG. 4A) includes a selectivelyactuatable valve body 56 having an internal mechanical drive (not shown)with an outwardly extending, axially rotatable stem 58. The stem 58 isconnected to a spherical valve ball 60 having a central passageway 62.The ball 60 is located within a tubular segment 64, which is receivedwithin an outer valve sleeve 66. The inboard end of sleeve 66 is securedto mounting plate 42 by means of threaded fasteners. It will be observedthat the central passageway 62 and the bore of segment 64 are of equaldiameter, and that the opposed inboard and outboard faces 68, 69 of thesegment 64 respectively define the fluid outlet 70 and fluid inlet 71 ofthe valve assembly 52. In preferred practice, the valve assembly 52 isan automated valve, which can be controlled as a part of an overalldigital control system for the preconditioner 20. However, other typesof valves may be used in this context.

The static mixing section 54 includes an upright tubular casing 72having a maximum internal diameter (FIG. 5), with an uppermost tubularsteam inlet 74 and an oblique water inlet 76, preferably equipped withan atomizer 77. A static mixer 78 is situated within casing 72 andincludes an elongated, stationary central shaft 15 80 with a pluralityof generally helical, outwardly extending plates 82 secured to the shaft80. The function of mixer 78 is to intensely mix incoming streams ofsteam and water, and any other desired additives, for delivery toinjection valve assembly 52. To this end, a pipe tee 84 is secured tothe bottom end of casing 72, and the transverse leg thereof isoperatively coupled to the inlet 71 of valve assembly 52 by means ofconventional piping 86.

The lower end of tee 84 is equipped with a pipe section 88, reducer 90,and condensate outlet pipe 92. The pipe 92 has an intermediate valve 94,which is controlled by solenoid 96. A resistance temperature probe 98 isoperatively coupled with pipe 92 below valve 94, and serves to measurethe steam condensate temperature and monitor the presence of live steamprior to start-up of the system; once the temperature reaches 100degrees C., the valve 94 closes and the system can start. Of course, theprobe 98 and solenoid 96 are connected to the overall digital controlsystem for the preconditioner 20 for automated control of valve 94.

An important aspect of the invention is the geometry of the injectionvalve assembly 52 and the injection aperture 43. In order tosubstantially reduce or even eliminate the possibility of plugging ofthe valve assembly 52, the diameters of the injection aperture 43,injection opening 43 a, valve ball passage 62, the bore of segment 64,the valve inlet 71, and the valve outlet 70 should all be at least about1 inch, and more preferably from about 1-2 inches, and areadvantageously all the same diameter. Furthermore, the axial distancebetween the fluid outlet 70 and the injection outlet opening 43 a shouldbe held to a minimum. This distance should be no more than about 3inches, preferably less than about 2 inches, still more preferably lessthan about 1 inch, and most preferably less than about one-half inch.

During the normal operation of preconditioner 20, dry ingredients arefed to the inlet 36 during rotation of the shafts 26, 28.Simultaneously, appropriate quantities of steam and/or water aredirected through the inlets 74, 76 and are thoroughly blended in casing72 during passage through static mixing section 54. This blended mixtureis passed into the injection valve assembly 52 through tee 84 and piping86, whereupon it is injected into the interior of housing 24 throughinjection inlet 43 a for mixing with the dry ingredients. During thissequence, the valve 94 is closed. When the temperature probe 98 detectsthe buildup of condensate above valve 94, the latter is opened to allowcollected condensate to drain from the system via pipe 92.

The injection of the blended mixture into housing 24 comprises the stepof conveying the blended mixture from the static mixer 78 to theinjection inlet 43 a using a conveying assembly including pipe 86, valveball 60, central passageway 62, and mounting plate 42. As depicted inFIG. 4A, the passageway of plate 42 defines the outlet of the conveyingassembly, which is adjacent to and in communication with the injectioninlet 43 a, where the internal diameters of the plate 42 passageway andthe injection inlet 43 a are less than the maximum internal diameter ofthe casing 72. By virtue of this arrangement, it will be appreciatedthat there is no contact between the blended mixture and the atmosphereduring the mixture-injecting step.

It will also be observed that the longitudinal axis of the pipe 86 istransverse to the longitudinal axis of the casing 72. In the illustratedembodiment, the longitudinal axis of the casing 72 is upright whereasthe longitudinal axis of the pipe 86 is horizontal.

Although the composite fluid injection assembly 22 has been illustratedand described in connection with a preconditioner, this assembly canalso be used in the context of single or twin screw extruders.Furthermore, improved fluid injection results can be obtained when usingthe individual components of the assembly 22. Hence, eitherpreconditioners or extruders may be equipped with fluid injection valveassemblies 52 or the static mixing sections 54 to achieve improvedresults. It is preferred, however, to employ the composite injectionassembly 22.

For example, FIG. 7 illustrates a twin screw extruder 100 equipped withfour fluid injection valve assemblies 52 secured to the inlet head 102of the extruder. The extruder 100 is itself of conventional design andincludes an elongated, tubular, multiple head extruder barrel 104 madeup of inlet head 102, intermediate head 106, and terminal head 108. Asillustrated, the inlet head 102 is equipped with a material inlet 110adjacent the input end of the barrel 104, whereas a restricted orificedie assembly 112 is provided at the outlet end of the barrel.Internally, the extruder 100 has a pair of elongated, axially rotatable,multiple-section extruder screws each having a central shaft withoutwardly extended helical flighting thereon (see FIG. 9). Materialdelivered to inlet 110 is subjected to increasing levels of temperature,pressure, and shear during passage through the extruder and suchmaterial is ultimately extruded through assembly 112

During the course of extrusion of many types of comestible materials, itis important that steam and/or water, with or without additionalingredients, be injected into the barrel where it is thoroughly mixedwith the previously preconditioned ingredients during the extrusioncooking process. In the embodiment of FIG. 7, four of the injectionvalve assemblies 52 are secured to inlet head 102 at respectivelocations where injection bores 114 are formed through the sidewall ofthe head 102, terminating in openings 114 a. A water and/or steam line116 is secured to the input of each valve assembly 52, in lieu of thepiping 86. FIG. 10 illustrates the extruder 100, but in this caseequipped with the previously described complete fluid injectionassemblies 22 mounted on the head 102. FIG. 9 further illustrates theinternals of the twin screw extruder 100, including the previouslymentioned pair of extruder screw assemblies, labeled as 120, 122,situated within an extruder barrel. Another option would be to have onlya single static mixer section 54 plumbed for connection with the fourinjection valves 52 illustrated in FIG. 10.

In the foregoing extruder embodiments, the fluid injection assemblieshave each included the fluid injection valve assemblies 52. In theseembodiments, the same geometrical considerations apply as in the case ofthe preconditioner embodiments. Specifically, in order to avoidplugging, the diameters of the passageway 62 and bore 117 should both beat least about ½ inch, and more preferably from about 1-2 inches, andare preferably of the same diameter. The axial distance between thefluid outlet 70 and the opening 114 a should be no more than about 3inches, preferably less than about 2 inches, still more preferably lessthan about 1 inch, and most preferably less than about one-half inch.

In other cases, use may be made of an injection assembly without aninjector valve. As illustrated in FIG. 5, a fluid injection assembly mayinclude the previously described static mixing section 54, with tee 84and related piping which is directly secured to a preconditioner and/orextruder barrel, as the case may be.

The use of composite fluid injection assembly 22 with preconditioner 20results in a number of important advantages not obtainable with priorfluid injection apparatus, typically making use of a plurality ofinjectors and associated manifolds, piping, and hoses. For example, thepreferred composite fluid injection apparatus gives at least thefollowing improvements:

-   -   Static Mixer—mixes/blends steam and water (and optional        additional ingredients), delivering superheated water to the        conditioning cylinder.        -   No mechanical mixing.        -   No Venturi mixing.    -   Water Injector to Static Mixer—Atomizes water to provide more        surface area to condense steam in the static mixer.    -   Automated Control Valve—Automated open/close valve that is        closely mounted to the body of the conditioning cylinder allows        for the efficient delivery of steam/water to the process, and is        mounted in a manner to minimize the distance between the valve        and the cylinder body to reduce injector plugging potential.    -   Condensate Resistance Temperature Detector—Determines the        buildup of condensate.    -   Condensate Solenoid Valve—Upon detection of condensate, the        solenoid valve opens to drain the condensate.    -   System Controls—Controls are tied into the overall extrusion        system control software, such as the Wenger APM System, for the        automated control of the valve and condensate temperature        detector.

The principal advantages of the fluid injection assemblies include:

-   -   Reduces the number of steam and water injection ports from        typically 5-6 for steam and water injectors (10-12 total) to        one.        -   Simplifies control of system for operators and            troubleshooting for maintenance            -   Reduces operator influence on system, allowing better                automated control.            -   Improves operation and product quality consistency.        -   Eliminates the need for multiple steam and water manifolds.            -   Improves sanitary design of the conditioning cylinder by                reducing the number of obstructions to clean around.        -   Reduces the number of valves, hoses, and injectors that have            to be maintained and replaced.    -   Location of the fluid injector valve on the preconditioner        housing or extruder barrel greatly reduces the potential for        injector plugging:        -   Increases equipment up time.        -   Improves process control.        -   Improves product consistency and quality.    -   Significant reduction in discharge steam vapor discharged from        the system.        -   Increase steam and water consumption on a per unit basis.        -   Reduces the food safety and sanitation risk from steam vapor            and associated fine food particulate matter going into the            atmosphere and potentially contaminating equipment and            environment.    -   Utilizes a static mixer to combine the process team and water:        -   Increases temperature of water to allow for better            absorption into the product.        -   Reduces steam vapor that can blow through the produce and            not be absorbed.    -   Higher product temperatures from the preconditioner        -   Improved adsorption of the steam and water inputs result in            higher product temperatures.        -   Achieves control point temperatures at lower steam and water            inputs.    -   Higher starch gelatinization (cook) values        -   Higher cook values during preconditioning provide            opportunity for higher final product cook values from            extruder.

As indicated, use of the fluid injection apparatus is particularlyimportant in the case of preconditioning of food or feed materials priorto extrusion thereof. In order to demonstrate the superiority of thepresent invention versus conventional fluid injection apparatus, aseries of test runs were carried out using the improved preconditionerof the invention equipped with the composite assembly 22 of theinvention, versus an otherwise identical preconditioner having thenormal multiple steam/water injectors along the length of thepreconditioner housing. In all cases, the individual comparative testsinvolved the same feed recipes (pet or aquatic feeds) with the samethermal energy inputs, retention times, and the like.

The test results confirm that the preferred apparatus of the inventionconsistently yields higher cook values (as measured by the extent ofstarch gelatinization) at a variety of preconditioner mixing intensitiesand feed rates. These improvements, coupled with the reduction in steamvapor venting from the apparatus of the invention and consequent betterenergy utilization, are salient features of the invention.

We claim:
 1. A method of treating a comestible material, comprising the steps of: passing said comestible material into and through an elongated housing presenting a material inlet, a spaced material outlet, and at least one axially rotatable shaft within the housing and having a plurality of outwardly extending mixing elements secured to the shaft; while said material is passing through said housing, delivering a fluid comprising steam and water into an injection inlet of said housing for mixing with the material, said fluid delivering step comprising the steps of separately directing individual quantities of steam and water into the casing of a static mixer, said casing having separate inlets for said separately directed individual quantities of steam and water, respectively, and presenting a maximum internal diameter, blending the steam and water within said static mixer casing to create a blended mixture, and then injecting the blended mixture into said housing injection inlet, said mixture-injecting step comprising the step of conveying said blended mixture from said static mixer to said housing injection inlet using a conveying assembly including a pipe assembly having an outlet adjacent to and in communication with said housing injection inlet, said pipe assembly outlet and said housing injection inlet having internal diameters less than the maximum internal diameter of said static mixer casing.
 2. The method of claim 1, said fluid consisting essentially of said steam and water.
 3. The method of claim 1, said injecting step comprising the step of directing the blended mixture through valve structure forming a part of said conveying assembly and comprising a shiftable valve member.
 4. The method of claim 3, said valve member being a rotatable ball valve.
 5. The method of claim 1, said water inlet having an atomizer.
 6. The method of claim 1, including the step of measuring the temperature of steam condensate from said static mixer, and permitting the delivery of said blended mixture into said housing only after the measured temperature reaches 100° C.
 7. The method of claim 1, including the step of directing said quantities of water into said quantities of steam at an oblique angle relative to the path of travel of the steam coming into the static mixer.
 8. The method of claim 1, including the step of preventing contact between said blended mixture and the atmosphere during said mixture-injecting step.
 9. The method of claim 1, said pipe assembly having an elongated delivery pipe presenting a pipe longitudinal axis, said pipe longitudinal axis being transverse to a longitudinal axis of said casing.
 10. The method of claim 9, said casing longitudinal axis being upright, and said pipe longitudinal axis being horizontal.
 11. A method of treating a comestible material, comprising the steps of: passing said comestible material into and through an elongated housing presenting a material inlet, a spaced material outlet, and at least one axially rotatable shaft within the housing and having a plurality of outwardly extending mixing elements secured to the shaft; while said material is passing through said housing, delivering a fluid comprising steam and water into said housing for mixing with the material, said fluid delivery step comprising the steps of separately directing individual quantities of steam and water into a static mixer, blending the steam and water within said static mixer to create a blended mixture, and then injecting the blended mixture into said housing, said fluid delivery step further comprising the step of measuring the temperature of steam condensate from said static mixer, and permitting the delivery of said blended mixture into said housing only after the measured temperature reaches 100° C.
 12. A method of treating a comestible material, comprising the steps of: passing said comestible material into and through an elongated housing presenting a material inlet, a spaced material outlet, and at least one axially rotatable shaft within the housing and having a plurality of outwardly extending mixing elements secured to the shaft; while said material is passing through said housing, delivering a fluid comprising steam and water into said housing for mixing with the material, said fluid delivery step comprising the steps of separately directing individual quantities of steam and water into a static mixer, blending the steam and water within said static mixer to create a blended mixture, and then injecting the blended mixture into said housing, said quantities-directing step including the step of directing said quantities of water into said quantities of steam at an oblique angle relative to the path of travel of the steam coming into the static mixer. 